Femtosecond coherence spectroscopy using spectrally selective differentialphotodetection

We present a novel. spectrally selective, detection scheme for pump-probe f emtosecond coherence spectroscopy (FCS) that attenuates the non-oscillatory background signal so that the coherent oscillations are more clearly revea led. The method is based on spectral dispersion of the probe beam after it has traversed the sample, followed by detection of spectrally specific port ions with a differential detector containing two balanced photodiodes. By a ppropriately choosing the spectral windows detected by each photodiode, we show how vibrational oscillations can be selectively enhanced or suppressed . Information about the phase behavior of the vibrational modes is also rev ealed using this detection scheme. (C) 2001 Elsevier Science B.V. All right s reserved.